Canola grain is valued primarily for its high-quality oil. Canola oil processing economics is hindered by the relatively low value of the non-oil portion of the canola seed, which constitutes over 50% of the mass of the incoming grain.
The meal from conventional canola crushing and solvent extraction has a low value, due to the presence of anti-nutritional compounds, and a low quality protein. Phytate, phenolics, and residual glucosinolates are common problems for feed and food from all the materials (meal, white flake, press cake, and whole seed), depending on the applications. Their impact on aqueous or alcohol based processes varies depending on the desired end product.
Canola or rapeseed consists of approximately 40% oil and 60% non-oil constituents. In commercial processing, most of the oil is removed from the seed by expelling and solvent extraction. In processing systems based on solvent extraction, the non-oil material initially exists as a solvent laden white flake or marc. Typically, solvent is removed from the white flake by a process that involves application of steam and heat to generate a final desolventized-toasted product called meal. The meal contains about 35% protein and is sold as a feed ingredient for inclusion in diets fed to a variety of classes of animals including swine, poultry and cattle.
Canola seed protein has excellent feeding value. The protein is rich in methionine and lysine, with a good balance of essential amino acids. Rapeseed protein concentrate had the highest protein efficiency ratio (PER) of all of vegetable protein sources reported. As such canola or rapeseed protein, in itself, can be considered to be exceptional in comparison to other plant proteins. Dephytinized rapeseed protein concentrate could replace high quality fishmeal in diets fed to rainbow trout without adversely affecting growth performance and feed efficiency of the fish.
However, monogastric animals do not fully utilize the protein feeding value of canola or rapeseed protein when the protein is supplied in the conventional form as part of the meal. Non-dehulled, desolventized, toasted canola meal contains high levels of fiber. Fiber has little nutritional value for animals such as fish, chickens and young pigs and thus dilutes the protein and energy content of the meal. Further, antinutritional factors, such as phenolics, associated with the meal may have a negative impact on the performance of monogastric animals such as pigs, chickens and fish. In addition, the toasting process typically employed during preparation of the final meal product decreases the protein solubility of the meal and has been shown to decrease lysine digestibility when fed to chickens.
Still further, canola meal also contains exceptionally high levels of phytic acid. Phytic acid is the storage form of phosphorus in the seed and is poorly digested by monogastric species. Phytic acid can form complexes with minerals, amino acids, and proteins and thereby decreases nutrient digestibility. Further, the phosphorus in the phytic acid molecule is largely unavailable to the animal and is voided with the feces. Given this poor digestibility of phytate-phosphorus, diets must be formulated with sufficient available dietary phosphorus to meet the requirements of the animal; this tends to increase the cost of the ration. In addition, undigested phosphorus in the manure can be damaging to the environment and is of considerable concern in areas of intensive livestock production. Overall, the high fiber and high phytate content of canola meal limits the feeding value as a protein source for monogastric animals.
Ruminant animals, such as cattle, can extract energy from fiber through fermentation in the rumen. Further, rumen microbes can efficiently hydrolyze phytate; thus, the potential for antinutritional effects and damage to the environment from dietary phytic acid is less of a concern in feeding ruminant animals. Highly soluble protein is rapidly hydrolysed and utilized by microbes in the rumen. Protein that is resistant to degradation in the rumen but is largely digested during subsequent passage through the small intestine has the highest protein feeding value for ruminant animals. Thus, as feed ingredients for ruminant animals, the highly soluble proteins in canola seed are of lower feeding value than the fraction of total canola proteins that are relatively insoluble.
Considerable prior work in this area has focused on methods to achieve efficient protein extraction from oilseed-based starting material followed by concentration or isolation of the protein into a single high valued product. For example, U.S. Pat. No. 5,658,714 relates to a soy protein isolate wherein defatted soy flour slurry is prepared and adjusted to a pH such that the protein becomes solubilized. U.S. Pat. No. 4,420,425 relates to a method of producing proteins from nonbinding oilseeds such as soybeans and peanuts by solubilization and ultrafiltration. U.S. Pat. No. 5,989,600 relates to a method for improving the solubility of vegetable proteins, which methods comprise treating the vegetable protein source with a phytase enzyme, and treating the vegetable protein source with a proteolytic enzymes.
Incidentally, the use of enzymes to increase the yield of oil from canola pressing and extraction is not a new idea. Previous work has shown that carbohydrases are effective in this role, but their cost is not supported by the incrementally improved yield. Use of phytase enzymes is also a well-established concept. A newer idea is to use a white-rot fungus to decrease the phenolic content of canola products. Phenolics likely contribute to excessive color and taste of canola protein products, so their removal could allow these to have a higher value.
U.S. Pat. No. 3,966,971 relates to vegetable protein source materials that are dispersed in water at a pH in the range of 2 to 6 with an acid phytase included therein. The acidic extract containing soluble protein is separated and dried to yield a solid protein. A protease can also be used to improve the characteristics of the protein.
U.S. Pat. No. 4,435,319 teaches that protein can be extracted from sunflower meal by treating an aqueous slurry of the meal with an acid at a pH between 4.0 and 7.0. The soluble and insoluble residues are separated, and the insoluble material is continually treated with an acid solution until the desired extraction of protein is attained. The extracted proteins are then recovered by precipitation or by ultrafiltration.
U.S. Pat. No. 3,635,726 describes a procedure for the production of a soy protein isolate by extraction of the soy starting material under alkaline conditions whereby the pH is above the isoelectric pH of glycinin. After separating the extract from the insoluble residue the pH of the extract is reduced to the isoelectric pH of glycinin to induce protein precipitation.
U.S. Pat. No. 4,418,013 relates to a substantially undenatured protein isolate formed from certain legumes and oil seeds, typically rapeseed (canola), by extracting protein from the source material with water and then diluting the resulting protein solution with more water. The dilution forms a dispersion of protein aggregates which are settled from the dispersion.
U.S. Pat. No. 4,889,921 relates to the use of pH changes and membrane filtration to extract and separate protein fractions from oilseeds. This method has been used on canola and mustard meals, with the general target of food-quality material.
WO 95/27406 teaches that phytase can be added to water suspension of a soy-based starting material. Under controlled conditions of pH and temperature the phytate content is reduced.
Tzeng et al. (Journal of Food Science 1990. 55:1147-1156) describe production of canola protein materials by alkaline extraction, precipitation, and membrane processing.
U.S. Pat. No. 2,762,820 to Sugarman (“Process for simultaneously extracting oil and protein from oleaginous materials”), for example, describes a process for simultaneously extracting oil and protein from oil seeds. Peanuts are exemplified. Whole peanuts are ground to a slurry in an aqueous alkaline solution. The pH is then lowered, and heat is applied. Subsequent steps are then used to separate the protein and the oil.
More recently, two approaches in the area of aqueous processing of canola involve the use of toasted or hexane-extracted meal or white flake as the feed material for aqueous extraction, and the use of mechanical methods to separate protein-rich materials from a mild aqueous extraction.
The technology of the first approach is described in WO 03/053157 A1; U.S. Pat. No. 5,844,086; WO 97/27761; and in U.S. Patent Application 2005/0031767 A1. In these approaches, an aqueous salt solution is used to solubilize proteins from defatted (hexane-extracted) canola meal, and the proteins are recovered by chilling to get a sticky “protein micellar mass.” Those patent references teach that the mild pH and low temperature extraction minimizes denaturing of the proteins and maximizes the quality of the protein product.
Defatted meal from dehulled grain has been used to reduce the color of the protein products. The published yields of the process are low, with less than 40% of the protein extracted. The products from this aqueous processing of canola and their functionality for food applications are described in WO 03/075673 A1; WO 03/034836 A1; and WO 02/089598 A1. There are three main canola proteins: 2S (napin—albumin), 7S, and 12S (cruciferin) protein. Micellar mass contains primarily the 7S protein, and the 2S goes preferentially to the filtered isolate product (material that was soluble after the first protein precipitation step). The 12S protein is in both products but is more likely to be in the protein micellar mass.
Regarding the second approach, U.S. Pat. No. 6,800,308 B2 and WO 2004/047548 A1 describe mainly mechanical methods to separate protein-rich materials from a mild aqueous extraction. This approach may also use phytase enzyme to dephytinize the material and may induce curdling with heat. The products of these processes are primarily used as animal feed, particularly fish feed, rather than human food markets.
US 2005/0136162 A1 describes aqueous milling combined with enzymatic treatment and heat to create a range of products isolated by centrifugation, evaporation, and filtration. Overall protein extractions of 71-76% in four different protein-containing fractions are reported therein in Examples 1 and 4.
Before the subject invention, it was not possible to profitably obtain saleable feed and food protein products out of canola presscake, whole seed, white flake, or meal via aqueous extraction.